1. Field of the Invention
The present invention relates to a process for manufacturing aminoalkylsilanes.
2. Description of the Background
A method for manufacturing aminoalkylsilanes, of which 3-aminopropyltriethoxysilane (AMEO) is an example, is known, wherein a chloroalkylsilane, such as 3-chloropropyltriethoxysilane (CPTEO), reacts in batches with an excess of ammonia or an organic amine in liquid phase, for example, with ammonia at T=90xc2x0 C., p=50 bar abs. and time=6 h. The product is then evaporated or concentrated and the pressure is reduced, at which point excess ammonia escapes and ammonium chloride is yielded in crystalline form. The evaporation process generally requires a period of time of over 10 hours. The ammonium chloride is usually separated from the crude product by filtration. The crude product is then distilled (DE-OS 27 49 316, DE-OS 27 53 124). However, a distinct disadvantage of this process is that, when the pressure is reduced over the product mixture, instances of caking occur, involving cakes of ammonium chloride or aminohydrochlorides. These cakes appear on the wall of the synthesis reactor, as well as on the stirring apparatus, and have a negative influence on heat transfer during the evaporation process. The deposits and caking require the plant to be at a frequent standstill, in which case the synthesis reactor has to be shut down, emptied, opened, filled with water in order to dissolve the ammonium salt crust, or freed of the cakes by mechanical means, then dried and closed.
EP 0 849 271 A2 also discloses the manufacture of 3-aminopropyltrialkoxysilanes from 3-chloropropyltrialkoxysilanes and ammonia by continuous operation. However, the disadvantage of this process is that even with a 100 fold excess of ammonia in relation to chloropropyltrialkoxysilane and an additional secondary reaction at 120xc2x0 C., a 95% maximum yield of crude silane mixture is only obtained from primary, secondary and tertiary aminosilanes.
Apart from the distillation and separation of precipitated ammonium chloride, additional pressure extraction is required for product separation. A need, therefore, continues to exist for an improved process of manufacturing 3-aminopropylalkoxysilanes.
Accordingly, one object of the invention is to provide an improved and more efficient process for manufacturing amninoalkylsilanes, particularly for the manufacture of 3-aminopropylalkoxysilanes.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a process for the manufacture of aminoalkylsilanes of formula I:
R1R2Nxe2x80x94(CH2)yxe2x80x94Si(OR3)3xe2x88x92nR4nxe2x80x83xe2x80x83(I)
wherein R2 and R2 are each independently, identical of different, hydrogen, aryl, arylalkyl or C1-4-alkyl; R3 and R4 are each independently, identical or different, C1-8-alkyl or aryl; y is 2, 3 or 4 and n is 0 or 1, 2 or 3, comprising:
reacting an organosilane of formula II:
Xxe2x80x94(CH2)yxe2x80x94Si(OR3)3xe2x88x92nR4nxe2x80x83xe2x80x83(II),
wherein X is Cl, Br, I or F; and R3, R4, y and n are each as defined above with ammonia or an organic amine compound of the formula:
HNR1R2xe2x80x83xe2x80x83(III),
xe2x80x83wherein
R1 and R2 are each as defined above with at least one of R1 and R2 not being hydrogen in a liquid phase;
evaporating ammonia or organic amine under reduced pressure while ammonium chloride or aminohydrochloride by-products, produced in the reaction of the first step, remains dissolved in the liquid phase;
transferring the product mixture after said evaporation to another vessel operated at a lower pressure level of than the second stage, and allowing ammonium chloride or aminohydrochloride to crystallize;
separating the crystalline ammonium chloride or aminohydrochloride from the crude product; and
distilling the crude product to produce purified aminoalkylsilane product.
It has now been discovered, surprisingly, that aminoalkylsilanes can be manufactured simply and economically by reacting an alkylarylsilane, such as 3-chloropropyltriethoxy silane (CPTEO), in a first process stage with an excess of ammonia or an organic amine used in excess in a liquid phase, and then evaporating ammonia or organic amine in a second process stage under reduced pressure, wherein a substantial portion of excess ammonia or organic amine escapes and ammonium chloride or predominantly aminohydrochloride remains, appropriately fully dissolved in a liquid phase. The product mixture from the second process stage is then transferred to a vessel, operated at a lower level of pressure than in the evaporation step, and ammonium chloride or aminohydrochloride crystallizes. The crystalline ammonium chloride or aminohydrochloride is separated from the crude product and finally the crude product is processed by distillation to provide purified aminoalkylsilane product.
The present invention, in particular, provides an effective method of producing aminoalkylsilanes having formula I above by the reaction of an organosilane having formula II shown above with ammonia or a nitrogen compound having formula III shown above.
Preferred suitable 3-chloralkylalkoxysilanes include 3-chloropropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropylmethyldimethoxysilane and 3-chloropropylmethyldiethoxysilane as the organosilane of formula II. However, other chloralkylalkoxysilanes, such as, for example, 3-chloropropyldiethylmethoxysilane or 3-chloropropylethylpropylethoxysilane, can also be employed in the present process.
In the process of the present invention ammonia, methylamine, ethylamine or diethylamine is preferably used as nitrogen containing constituent having formula III.
Examples of products of the present invention which can be manufactured simply and economically include 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropylmethyldiethoxysilane and N-methyl-3-aminopropyltrimethoxysilane, to name but a few.
In the process of the present invention organosilanes of formula II and ammonia or an organic amine of formula III in liquid form are usually fed to a pressure reactor, in which case it is suitable to set the molar ratio of chloralkylalkoxysilane to ammonia or organic amine compound at 1:10 to 1:50. In the first process stage conversion generally takes place at a pressure of 25 to  less than 100 bar abs. and at a temperature of 50 to  less than 110xc2x0 C., wherein conversion is almost complete. In addition, the almost complete portion of ammonium chloride or aminohydrochloride by-product remains dissolved in the liquid phase. Preferably more than 99%, in particular preferably 99.9% to 100%, of the ammonium chloride or aminohydrochloride resulting from the reaction remains dissolved in the liquid phase of the first stage. The resulting product mixture is then transferred to the second process stage, in which case the second process stage is performed at a substantially lower pressure than the first process stage. In the process, considerable quantities of ammonia are flashed removed, for example, 50% to 80% by weight of the excess ammonia or organic amine. This removal of excess reactant is effected by using an operating procedure in which the pressure transitions from 50 to 15 to 20 bar abs.
The second evaporative stage is normally performed at pressures of  greater than 10 to  less than 50 bar abs., preferably 11 to 35 bar abs., more preferably 13 to 25 bar abs., and most preferably 15 to 20 bar abs., and at a temperature of  greater than 10 to  less than 110xc2x0 C., preferably 20xc2x0 C. to 95xc2x0 C., more preferably 30xc2x0 C. to 85xc2x0 C., and most preferably 35xc2x0 C. to 80xc2x0 C., so that ammonium chloride or aminohydrochloride remains almost completely dissolved in a liquid phase This procedure enables problems which arise from the accumulation of solids to be prevented as desired. In general, the evaporation times result from the excess quantities of ammonia and amine of the reaction and the available evaporation apparatus, evaporator surfaces and the like as well as the structure of the plant being used. With the process of the present invention there is a large degree of freedom for selecting appropriate and cost-effective plant components for the above-mentioned evaporation processes because of the practically solids-free operation in the second evaporative stage. The product dwell time in the second evaporative stage ranges from 0.1 to 4 hours, preferably from 0.1 to 2 hours, in particular from 0.1 to 1 hour.
After the evaporation step, the crystallization of the ammonium chloride or aminohydrochloride by-product occurs in a the third step, which is conducted, for example, in a crystallizer equipped with an agitator. Crystallization is generally conducted at a pressure below the final pressure of the second evaporative stage, preferably at 1 to 6 bar abs., wherein the solubility limits of ammonium chloride or amine hydrochloride are not reached. These by-products are obtained particularly gently in crystalline form. The operating temperature of the crystallization stage is as a rule in the range of 20xc2x0 C. to 60xc2x0 C. The solids can be separated from the product in a know manner and then the crude product processed by distillation.
The process according to the present invention is generally carried out as follows: In a first process stage an organosilane of general formula II is caused to react with excess ammonia or organic amine in a liquid phase and the resulting product mixture is transferred to the second process stage, where ammonia or organic amine is evaporated under reduced pressure and resulting ammonium chloride or aminohydrochloride remains dissolved in the liquid phase. The product mixture from the second process stage is then transferred to a third process stage, operated at a lower level of pressure than the second stage, and ammonium chloride or aminohydrochloride is crystallized out and separated from the crude product. The mixture can be separated by filtering. The resulting crude aminoalkylsilane product can be processed by distillation.
The process of the present invention is distinguished by the following advantages:
The batch time in the present process can be at least halved, compared to that disclosed in DE-PS 27 49 316 or DE-OS 27 53 124, resulting in a doubling of the plant capacity.
Caking usually no longer appears in the synthesis reactors.
Almost no solids accumulate in the second evaporative step, which allows power to be introduced to the process at a favorable point to evaporate the majority of ammonia or organic amine.
The pressure graduation of the process stages of the present invention allows the use of more cost-effective apparatus for broad processing areas in process stages 2 or 3, in comparison to the respective preceding process steps.
Smaller apparatus can also be utilized in subsequent steps because of the reduced quantities of ammonia or organic amine, as compared to the preliminary step.